Resources in process algebra
The Algebra of Communicating Shared Resources (ACSR) is a timed process algebra which extends classical process algebras with the notion of a resource. It takes the view that the timing behavior of a real-time system depends not only on delays due to process synchronization, but also on the availability of shared resources. Thus, ACSR employs resources as a basic primitive and it represents a real-time system as a collection of concurrent processes which may communicate with each other by means of instantaneous events and compete for the usage of shared resources. Resources are used to model physical devices such as processors, memory modules, communication links, or any other reusable resource of limited capacity. Additionally, they provide a convenient abstraction mechanism for capturing a variety of aspects of system behavior. In this paper we give an overview of ACSR and its probabilistic extension, PACSR, where resources can fail with associated failure probabilities. We present associated analysis techniques for performing qualitative analysis (such as schedulability analysis) and quantitative analysis (such as resource utilization analysis) of process-algebraic descriptions. We also discuss mappings between probabilistic and non-probabilistic models, which allow us to use analysis techniques from one algebra on models from the other.